Luminescent display tube anode assembly comprising anode segments each having a tungsten carbide conductive layer

ABSTRACT

An anode assembly for a luminescent display tube comprises a substrate and a plurality of anode segments. The anode segments have layers of a luminescent material deposited in respective recesses formed in the substrate in conformity with the anode segments. A layer of tungsten carbide is disposed underlying each of the luminescent material layers.

Kobayakawa et al.

1 LUMINESCENT DISPLAY TUBE ANODE ASSEMBLY COMPRISING ANODE SEGMENTS EACH HAVING A TUNGSTEN CARBIDE CONDUCTIVE LAYER [75] Inventors: Masaki Kobayakawa; Kazufumi Yawata, both of lzumi, Japan [73] Assignee: Nippon Electric Kagoshima, Ltd.,

Kagoshima, Japan [22] Filed: May 8, 1974 [21] Appl. No.: 468,065

{30] Foreign Application Priority Data May 15, 1973 Japan 48-57504 [52] U.S. Cl. 313/496; 313/311; 313/355 [51] Int. Cl. H01J 1/66; l-lOlJ 63/02 [58] Field of Search 313/496, 497, 355, 311

[451 Sept. 16, 1975 [56] References Cited UNITED STATES PATENTS 3,504,213 3/1970 Hix et a]. 313/355 X 3,737,705 6/1973 Takeda et a1 313/496 Primary Examiner-Palmer C. Demeo Attorney, Agent, or Firm-John M. Calimafde 5 7 ABSTRACT An anode assembly for a luminescent display tube comprises a substrate and a plurality of anode segments, The anode segments have layers of a luminescent material deposited in respective recesses formed in the substrate in conformity with the anode segments. A layer of tungsten carbide is disposed underlying each of the luminescent material layers.

1 Claim, 2 Drawing Figures z t 'xtk ff I l I I I I I z I l I Z I I 1 I z I LUMINESCENT DISPLAY TUBE ANODE ASSEMBLY COMPRISING ANODE SEGMENTS EACH HAVING A TUNGSTEN CARBIDE CONDUCTIVE LAYER DISCLOSURE OF THE INVENTION BACKGROUND OF THE INVENTION This invention relates to electronic displays and, more specifically, to an anode assembly or structure for a luminescent display tube, also called a fluorescent display tube or a phosphor indicator tube. The invention is particularly concerned with an anode assembly for a luminescent display tube of the multi-digit or multi-figure type.

As described in U.S. Pat. No. 3,508,101 or No. 3,619,694, a tube of the subject kind comprises an evacuated sealed envelope; an anode assembly within the envelope and having a base plate or substrate formed of an insulating material and provided with a plurality of luminescent anode segments; a cathode disposed in front of the segments for thermally emitting electrons; a grid between the segments and cathode; and structure for supplying electric potentials between the cathode and grid and between the cathode and selected of the anode segments to have the electrons distributed substantially uniformly on the selected anode segment to render the anode segment luminescent. The cathode-anode potential may simultaneously be ap plied between the cathode and selected ones of the anode segments to make the selected anode segments luminesce together. Conforming with the anode segments, a plurality of recesses or grooves are formed in the substrate in a geometric configuration and dimension corresponding to one or more sets of figures to be selectively displayed. Each anode segment comprises a layer or film of an electroconductive material on the bottom surface of the recess and in contact with the anode segment voltage supplying structure. The anode segment further comprises a layer or film of a luminescent material covering the electroconductive material layer.

In sophisticated luminescent display tubes of the type described, the electroconductive material layers were made by spraying graphite onto the substrate or otherwise coating the substrate with graphite. In recent luminescent display tubes, particularly in those of the multidigit or multi-fi'gure types, it has become the practice to resort to tungsten metallizing on forming the electroconductive material layers in view of the raised efficiency of manufacture derived thereby. The displays of these recent tubes, however, are not as bright as those attained with the sophisticated tube type having the graphite conductive layers, The tungsten metallized layers may be covered with graphite layers to increase the brightness of the display. However, this detracts from simplicity of manufacture, and renders it impossible to utilize automated equipment for manufacture.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an anode assembly for a luminescent display tube which is capable of providing a bright display, and which may be manufactured as simply as the recent luminescent display tubes mentioned above.

An anode assembly for a luminescent display tube in accordance with the instant invention comprises a substrate and a plurality of anode segments. The anode segments have layers of a luminescent material disposed in respective recesses formed in the substrate in conformity with the geometric configuration of the anode segments. The anode assembly comprises a layer of tungsten carbide underlying each of the luminescent material layers.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view depicting a set of anode seg ments; and

FIG. 2 is a cross-sectional view of an embodiment of the instant invention, taken at section 22 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, an anode assembly for a luminescent display tube comprises a substrate 11 of an insulating material on which a set of anode segments 12 is disposed. In the example illustrated, seven anode segments :1, b, c, d, e,f, and g are arranged substantially in a figure eight pattern to display any desired one of the numerals 0 through 9. An additional anode segment It serves to display the number 4 in a more usual form. An anode segment DP for a decimal point is also employed.

The substrate 11 comprises a first base plate 21 having holes formed therethrough in conformity with the geometric configuration of the anode segments 12 and a second base plate 22 having a plurality of electroconductive layers 23 formed on one of its surfaces and extending beyond the cross-sectional areas of the respective holes. Each of the electroconductive layers 23 has a lead wire portion 24 extending through the second base plate 22 to the other surface thereof. The sub strate 11 further comprises a third base plate 26 on which a plurality of leads 27 are formed for electrically contacting the respective lead wire portions 24. The anode segments 12 comprise the electroconductive layers 23, and a layer 29 of a luminescent material covers each of the electroconductive layers 23. The base plates 21, 22, and 26 may be made of glass or a ceramic material.

After the base plates 21, 22, and 26 are stacked in the manner depicted, the holes of the first base plate 21 become recesses or grooves formed in the substrate 11. The electroconductive layers 23, together with the lead wire portions 24, may be formed by metallizing or printing. The leads 27 may also be formed by metallizing or printing. The luminescent material layers 29 may be formed by deposition in the respective recesses, or by subjecting the luminescent material to electrodeposition. It will be noted that the exposed surface of each luminescent material layer 29 is recessed to provide an inwardly directed area 30 coextensive with the side or peripheral surface of the associated recess.

For use in a luminescent display tube of the above considered recent type, the base plates 21, 22, and 26, the electroconductive layers 23, and the leads 27 may preferably be formed by screen printing a tungsten paste on green tapes and cofiring the paste and the tapes into an integral substrate 11 having the conductive portions 23, 24 and 27. In any event, the holes of the first base plate 21 become the recesses conforming in geometric configuration with the anode segments 12. The screen printing and co-firing techniques facilitate manufacture of an anode assembly for a luminescent display tube, particularly for a luminescent display tube of a multi-digit or multi-figure type. Use of a single tungsten metallized layer for each anode segment has, however, been objectionable from the view point of the relative lack of brightness of the display.

In accordance with this invention, the electroconductive layers 23 are made of tungsten carbide. Screen printing and co-firing techniques are well applicable to this material. In addition, an anode assembly comprising tungsten carbide conductive layers 23 raises the brightness level of the display by a surprising, very marked amount. With a tube made in accordance with the instant invention, it has been confirmed that the display brightness is about 1.5 times that achieved with the conventional tungsten layers. Because of the feasi bility of utilizing processes similar to those employed for tungsten metallized layers used in the recent anode assemblies. it will be appreciated that the anode assembly according to this invention does not adversely affect simplicity of manufacture. and is specifically suited for an anode assembly for use in a multi-digit or multifigure luminescent display tube where is it necessary to form a great number of such segments.

What is claimed is:

1. An anode assembly for a luminescent display tube, said assembly comprising a substrate and a plurality of anode segments having layers of a luminescent material disposed in respective recesses formed in said substrate in conformity with a desired configuration of said anode segments, wherein the improvement comprises a layer of tungsten carbide underlying each of said luminescent material layers. 

1. AN ANODE ASSEMBLY FOR ALUMINESCENT DISPLAY TUBE, SAID ASSEMBLY COMPRISING A SUBSTRATE AND A PLURALITY OF ANODE SEGMENTS HAVING LAYERS OF A LUMINESCENT MATERIAL DISPOSED IN RESPECTIVE RECESSES FORMED IN SAID SUBSTRATE IN CONFORMITY WITH A DESIRED CONFIGURATION OF SAID ANODE SEGMENTS, WHEREIN THE IMPROVEMENT COMPRISES A LAYER OF TUNGSTEN CARBIDE UNDERLYING EACH OF SAID LUMINESCENT MATERIAL LAYERS. 